Hot tubs or spas, wherein water in a relatively small vessel is circulated and heated to elevated temperatures, have come into considerable popularity in recent years. The spas are often used in the evening to provide relaxation after a day's work, but in general, they are not provided with underwater lights. Therefore, many people carry flashlights for safety in stepping into and out of the water, and to see if there are any foreign objects on the bottom. In addition, because of the elevated temperatures to which these spas are heated, usually above 100.degree. Fahrenheit, it is highly advantageous to have a thermometer which enables one to determine the water temperature at night. Further, in connection with water sports generally, there is demand for electrical devices, such as lanterns or radios which are buoyant and watertight.